Bimetallic driven time delay relay



Dec. 3, 1968 R. E. PROUTY BIMETALLIC DRIVEN TIME DELAY RELAY 2 Sheets-Sheet 1 Filed Aug 8, 1966 Dec. 3, 1968 R. E. PROUTY BIMETALLIC DRIVEN TIME DELAY RELAY 2 Sheets-Sheet 2 Filed Aug. 8, 1966 NORM/1 1 1 r Combat So? [VAPOR/ITO? fifliz for: Rober/ E Prozzt United States Patent 3,414,859 BIMETALLIC DRIVEN TIME DELAY RELAY Robert E. Prouty, Logansport, Ind., assignor to Essex Wire Corporation, Fort Wayne, Ind., a corporation of Michigan Filed Aug. 8, 1966, Ser. No. 570,814 8 Claims. (Cl. 337-51) ABSTRACT OF THE DISCLOSURE A bimetallic driven time delay relay switch. A bimetallic strip drives a plate with a ratchet mounted thereon back and forth as the strip snaps between its hot and cold positions. Each time the bimetallic strip shifts from the hot to the cold position, the ratchet engages a fixed pawl and is rotated one increment. After the ratchet has advanced a predetermined number of increments, a cam lobe attached to the ratchet engages with and closes a first switch as the bimetallic strip moves to its hot position. This first switch thereafter activates the bimetallic heater circuit and simultaneously closes a controlled external circuit. The heater circuit may be broken by a second switch, causing the ratchet to advance one increment upon cooling of the bimetallic strip, thereby disengaging the cam lobe from the first switch.

This invention relates to time delay switches and, more particularly, to a novel switch adapted to open or close an electrical circuit at a predetermined time after the switch is energized.

Time delay switches are useful in a variety of applications. In an air-conditioning system, for example, it is desirable to prevent the compressor motor from being re-energized until a predetermined delay period has elapsed after the motor is turned off. Similarly, in highpower vacuum tube circuits, it is desirable to prevent energization of the tube plates until the filaments have been brought to operating temperature.

A simple and inexpensive, yet highly reliable, interval timer may be constructed using a bimetallic element mounted for snap-action movement between hot and cool positions. An electric heater positioned adjacent the bimetallic element is energized whenever the element is in the cool position and de-energized when the element is in the hot position. The bimetallic element consequently alternates between the two positions. This oscillating bimetallic element may then be coupled to a ratchet wheel which advances by an incremental amount each time the bimetallic element snaps from one of the two positions to other. An output switch may be coupled to the ratchet wheelsuch that the switch is actuated after the ratchet has been advanced by predetermined, plural number of increments. An electro-mechanical time delay switch of this type is shown in US. Patent 3,202,842 which issued Aug. 24, 1965, to H. A. Sherwood.

In the prior art thermal switches of the type shown in the Sherwood patent, the output switch is actuated only momentarily since the ratchet wheel continues to rotate under the impetus of the oscillating bimetallic element. Latching relays or the like must accordingly be used where a sustained output from the time delay switch is required.

It is accordingly a general object of the present invention to provide a simplified time delay switch having a control input and a switched output wherein the switched output is actuated after a predetermined delay interval following the initial energization of the control input and continues to be actuated until the control input is de-energized.

It is a further object of the invention to provide a time delay switch which automatically resets whenever the control input is de-energized.

In a principal aspect, the present invention takes the form of an improved thermal time delay switch which includes a bimetallic element mounted for snap-action movement between hot and cool positions and a ratchet wheel which is advanced each time the bimetallic elements snaps from the hot to the cool position. According to a principal feature of the invention, switching means are included for maintaining the energization of the electrical heater adjacent the bimetallic element whenever the bimetallic element is in the hot position and the output switch is actuated. Since the ratchet wheel is adapted to be advanced upon cooling of the bimetallic element, termination of the electrical input to the bimetallic element cools the element and allows the switch to be advanced and automatically reset. The arrangement contemplated by the present invention is particularly adapted for use in conjunction with an air-conditioning system to prevent the compressor motor in such systems from being re-energized until a predetermined time interval has elapsed after the compressor motor has been turned off.

In a preferred embodiment of the invention, the ratchet wheel is mounted upon a shuttle plate, the plate being in turn mounted for sliding, reciprocating motion in a support frame as the bimetallic element moves from one position to the other. A projecting pawl atfixed to the support frame advances the ratchet wheel as the bimetallic element snaps from the hot to the cold position. A cam wheel is mounted coaxially with the ratchet wheel and includes a projecting lobe which engages with the controlled switch as soon as the ratchet has been advanced by a predetermined number of increments. The cam is also adapted to close a second switch which maintains the energization of the bimetallic heating element whenever the controlled switch is actuated even though the bimetallic element is in the hot position where the heating element would normally be de-energized.

These and other objects, features and advantages of the present invention may be more clearly understood through a consideration of the following detailed description. In the course of this description, reference will frequently be made to the attached drawings, in which:

FIGURE 1 is a side elevational view of a preferred embodiment of the invention;

FIGURE 2 is a bottom view looking upward toward the underside of the arrangement shown in FIGURE 1;

FIGURE 3 is a partial perspective view of the movable portion of the embodiment shown in FIGURES 1 and 2;

FIGURE 4 is a schematic diagram illustrating typical circuit connections for the switch shown in FIGURES l, 2 and 3;

FIGURES 5 through 8 show four different positions for the switch shown in FIGURES 1, 2 and 3; and

FIGURE 9 is a schematic drawing illustrating a typical application of the invention to provide time delay in an air-conditioning system.

The time delay switch shown in FIGURES 1 through 3 includes a base plate indicated generally at 11 through which five electrical terminal plugs 13 through 17 project. A dust cover indicated generally at 20 in FIGURE 1 may be employed to enclose the switch. Electrical connections are made between terminal plugs 13 through 17 and switch blades 21 through 26 through a mounting block indicated generally at 30. The mounting black 30 comprises a series of wafers which hold switch blades 21 through 26 insulated one from another and extending downwardly. Switch blades 22 and 25 are movable in response to the motion of a sliding shuttle plate indicated generally at 32 and a cam wheel 33 mounted thereon. The lower extremity of the movable switch blades 22 and 25 extend 3 respectively through rectangular openings 36 and 37 in the shuttle plate 32.

As seen in FIGURE 3, the shuttle plate 32 includes outwardly projecting end sections 41 and 42 which pass through openings in the downwardly extending flanges 44 and 45 respectively. Flange 45 is aflixed to a flange 47 which, together with flange 44, forms part of a shaped bracket indicated generally at 50 in FIGURE 1. The bracket 50 is aflixed to the base plate 11 by means of a pair of diagonally oriented bolts 51 and 52, the placement of which is seen more clearly in FIGURE 2.

The projecting end 41 of shuttle plate 32 is aflixed to a bimetallic element indicated generally at 60 which is mounted for snap-action at its ends by a bracket shown generally at 63. The bimetallic element is retained between a shoulder on end section 41 and a retaining screw 64. The bimetallic element 60 is covered with a coil of heating wire shown generally at 65.

Typical electrical connections for the time delay switch shown in FIGURES 1 through 3 are shown in FIGURE 4. The switch includes three external terminal pairs 66, 67 and 68 which are shown extending from the dotted rectangle 69. The input voltage, which may be either AC. or D.C., is applied across terminal pair 66. Heating element 65 is connected across terminal pairs 66 in series with the switch formed by blade arms 21, 22, and 23. The heating element is accordingly energized when movable blade 22 contacts either blade 21 or 23. The normally OFF output terminal pair 67 is connected to the input terminals 66 through the normally open switch blades 24 and 25 while the normally ON terminals are connected to the input terminals through the normally contacting blade arms 25 and 26.

As current is passed though the heating wire 65 to increase the temperature of the bimetallic element 60, the element 60 snaps to an outwardly bowed position indicated in phantom at 60 in FIGURE 2. As the bimetallic element 60 snaps between its hot and cold positions, it carriers with it the shuttle plate 32.

As best seen in FIGURE 5, when the bimetallic element 60 is cool, one edge of the opening 36 in shuttle plate 32 normally bears against the switch blade 22, holding blade 22 in contact with blade 23. In addition, the switch blade 26 is bent to one side such that it is normally in contact with the switch blade 25.

As the bimetallic element 60 is heated and snaps to its hot position, the shuttle plate 32 moves such that the other edge of opening 36 carries the switch blade 22 to a position spaced apart from both blades 21 and 23, as shown in FIGURE 6, opening the circuit supplying current to the heating wire 65. Switch blade 25 carries a plunger element 70 at its lower extremity which is positioned to bear against but is not attached to the switch blade 22. Thus, as the switch blade 22 is moved away from blade 23, as shown in FIGURE 6, its end becomes spaced from the plunger 70. The combination of switch blades 22 and 23 constitute switching means for supplying current to the bimetallic heating wire 65 when element 60 is in the cold position and for de-energizing the heating element 65 whenever the bimetallic element 60 is in the hot position.

As the shuttle plate 32 is carried back and forth by the bimetallic element 60, a ratchet wheel 71, clearly seen in FIGURES 2 and 3, is advanced. Ratchet wheel 71 engages with a pawl 72 which is fixedly mounted on the sliding shuttle plate 32. A second pawl 73, one end of which is mounted by means of a rivet 74 between flanges 45 and 47, engages with the ratchet wheel 71 to rotate it in a counterclockwise direction as seen in FIGURE 2 as the bimetallic element moves from the hot to the cold position. The ratchet wheel 71 advances only when the bimetallic element 60 moves from the hot to the cold position. A rigid flange member 75 insures the engagement of the flexible pawl 73 with the ratchet wheel 71.

Ratchet wheel 71 is aflixed to the cam wheel 33 such that these wheels rotate together about an axle 77 afiixed to the shuttle plate 32. The cam wheel 33 includes three lobes 81, 82 and 83 which extend radially outward. The lobes 81, 82 and 83 are positioned in alignment with every fourth tooth in the ratchet wheel 71. Thus, every fourth time the shuttle plate 32 is moved as the bimetallic element travels beween its hot to its cold position, one of the lobes 81, 82 or 83 is positioned over the opening 37, as shown in FIGURE 7. Consequently, as the bimetallic element again moves from its cold to its hot position, the appropriately aligned lobe bears against the switch blade 25, moving it into contact with the switch blade 24, as shown in FIGURE 8. Simultaneously, plunger 70 moves switch blade 22 into contact with blade 21. The combination of switch blades 24, 25 and 26 accordingly constitute the controlled switched output of the device, the connection of blade 25 being transferred from blade 26 to blade 24 after a predetermined delay interval has elapsed.

The movement of blade 22 into contact with blade 21 under the force from plunger 70 provides means for energizing the heating element 65 whenever the controlled output switch is actuated even though the bimetallic element 60 is in its hot position. This continued energization of heating element 65 prevents further movement of bimetallic element 60. Thus, the arrangement provides continued energization of the output terminals 67 shown in FIGURE 4 until input power is removed from terminals 66. When power is terminated, the bimetallic element 60 snaps to its cool position, advancing cam member 33, and resetting the timer.

FIGURE 9 of the drawings shows a typical application of the timing device according to the invention. The time delay switch is shown generally at 69 and has an input 66 and an output 67 which correspond to the teminals shown in FIGURE 4. A source of alternating current energy is connected to the input terminal pair 66 through a switch 181. The output terminal pair 67 is connected to supply a delayed voltage to the motor 183 which drives a compressor 85. Compressor 85 accepts the vapor from an evaporator 87 through a conduit 88. The pressurized vapor is applied to a condensor 90 through a conduit 91. Fluid flows from the condensor 90 to the evaporator 87 through a conduit 93. The expansion which takes place within evaporator 87 cools the surrounding area. During operation of the air-conditioning system illustrated in FIGURE 9, a substantial pressure difference develops between the conduits 88 and 91. Should the drive motor 183 be stopped and restarted before the pres sure within these conduits is allowed to equalize, an unusual starting load is placed upon the motor 183. Accordingly, in order to allow a smaller motor to be used successfully, it is desirable that the motor be prevented from restarting for a predetermined time after it has stopped. This objective is accomplished by the time delay unit indicated at 69 in FIGURE 9. Whenever the switch 181 is closed, the time delay device 69 must completely cycle through a predetermined interval before the motor 183 will be energized. Consequently, if the switch 181 is opened for a suflicient time to allow the bimetallic element 60 within the timing device to cool, the closure of switch 181 is then ineffective to restart the motor 183 until the predetermined delay period has elapsed.

It is to be understood that the embodiment of the invention which has been described is merely illustrative of one application of the principles of the invention. Numerous modifications may be made by those skilled in the art without departing from the true scope and spirit of the invention.

What is claimed is:

1. In combination:

a bimetallic element mounted for snap-action movement between hot and cool positions,

electrically ener'gizable means for heating said bimetallic element,

a ratchet-wheel and pawl, said ratchet-wheel being mounted for unidirectional rotation about an axis,

means coupling said ratchet-wheel and said bimetallic element for advancing said ratchet-wheel by an incremental amount each time said bimetallic element snaps from said hot to said cool position,

a first switch responsive to the motion of said bimetallic element for energizing said heating means whenever said bimetallic element is in said cool position,

a second switch,

means coupled to said ratchet for actuating said second switch whenever said ratchet is advanced by a predetermined plural number of increments, and

switching means for maintaining the energization of said heating means whenever said bimetallic element is in said hot position and said second switch is actuated.

2. A combination as set forth in claim 1 including an electrical input circuit and an electrical outlet circuit and wherein said electrically energizable means for heating said bimetallic element is connected through said first switch to said input circuit and wherein said output circuit is connected to said input circuit through said second switch 'whereby the de-energization of said input circuit allows said bimetallic element to cool to reset said ratchet wheel to a starting position.

3. A thermal time delay switch comprising, in combination:

a bimetallic element mounted for snap-action movement between hot and cool positions,

an actuating member coupled to said bimetallic element and mounted for incremental movement each time said bimetallic element snaps from said hot to said cool position,

electrically energizable means for heating said bimetallic element, switching means coupled to said bimetallic element for energizing said electrically energizable means whenever said bimetallic element is in said is advanced by a predetermined plural number of in- I crements, and

switching means for maintaining the energization of said electrically energizable means whenever said bimetallic element is in said hot position and said controlled device is simultaneously actuated.

4. A thermal time delay switch as set forth in claim 3 wherein said actuating means comprises a ratchet wheel mounted on a shuttle plate, said shuttle plate being mounted for sliding movement upon a support frame in response to movement of said bimetallic element.

5. A thermal time delay switch as set forth in claim 4 including a pawl mounted on said support frame and projecting into a position of engagement with said ratchet wheel.

6. A thermal time delay switch as set forth in claim 3 wherein said frame includes a mounted, fixed pa wl adapted to engage said ratchet Wheel, and said bimetallic element is fixedly attached to said shuttle plate such that said plate and ratchet thereon move in unison with said bimetallic element, said ratchet engaging said fixed palwl to advance one increment whenever said element changes from hot to cold position.

7. A thermal time delay switch as set forth in claim 3 wherein said bimetallic element is rigidly fixed at either end of said strip, said strip having a center portion which is fixed to said plate by fastening means, said center portion bowing on opposite sides of a straight line between said fixed ends to assume said hot and said cold positions.

8. A thermal time delay switch as set forth in claim 3 wherein said plate includes .at least one opening, and said switching means includes at least one blade switch passing partially through said opening, said blade switch being activated by engagement with said opening as said plate is activated by said bimetallic element.

References Cited UNITED STATES PATENTS 3,202,842 8/1965 Sherwood.

BERNARDA. GILHEANY, Primary Examiner.

R. COHRS, Assistant Examiner. 

